Boiler construction

ABSTRACT

A boiler is provided, inside the water tubes or water jackets thereof, with a lining to its firebox or combustion chamber in the form of sheets or pads of mineral wool fiber enclosed between refractory steel grids, and with a refractory filter sheet of cloth woven of ceramic or mineral fiber filaments, permeable to gases but capable of holding back particulate material, the filter sheet extending over a major part of the exit from the combustion chamber and defining beyond it a heat exchange chamber in which the gases of combustion largely freed of particulate matter pass over heat exchange surfaces of the boiler water jackets or water tubes.

Uite

tates Patem Herzberg Feb. 15, 1197 2 [54] BOILER CONSTRUCTIGN 3,336,7168/1967 Scheppers ..126/144 X [72] Inventor: Claude Herzberg, BYOB,France FOREIGN PATENTS OR APPLICATIONS [731 Assigneel Swim PmduilsReimmires, 610,978 12/1960 Canada ..126/144 Paris, France [22] Filed:Sept. 26, 1969 Primary Examiner-Edward G. Favors pp No: 861,415An0meyPennie, Edmonds, Morton, Taylor and Adams [57] ABSTRACT [30]Foreign Application Priority Data A boiler is provided, inside the watertubes or water jackets Sept. 30, 1968 France ..168135 thereof, with alining to its firebox or combustion chamber in the form of sheets orpads of mineral wool fiber enclosed U-So CL R, between refractory steelgrids and a refractory filter [Sll -F23m 9/06 sheet of cloth woven ofceramic or mineral fiber filaments, [58] Field Of Search ..l 10/97, 98,8 A; 126/144 permeable to gases but Capable of holding back particulatematerial, the filter sheet extending over a major part of the [56]References Cited exit from the combustion chamber and defining beyond ita UNITED STATES PATENTS heat exchange chamber in which the gases ofcombustion largely freed of partlculate matter pass over heat exchangesur- 2,245,322 6/ 1 941 Bork 122/ 1 56 faces f the boiler water jacketsor water tubes 2,658,742 11/1953 Sutter et al. ....110/8 X 3,324,8456/1967 White ..110/97 X 7 Claims, 1 Drawing Figure q g I I I: l C 2 --fI l W s m N BOILER CONSTRUCTION The present invention pertains toimprovements in boilers, both for domestic heating and for industrialpurposes, the invention permitting a substantial reduction in thequantity of unburned fuel particles which appear in the exhaust gasestherefrom.

Oil-fired boilers for central heating purposes have the shortcoming thatthe smoke therefrom contains varying amounts of unburned solids, withconsequent varying color of the smoke.

In order to measure easily the quantity of solids in smoke there isemployed a so-called Bacharach apparatus in which a specified volume ofsmoke is caused to pass through a filter paper on which the solids arerecovered. By means of a colorimetric measurement of the paper there isobtained an index number on a scale extending from zero for no depositto for the case in which the paper has been rendered black and opaque.In practice new boilers in good condition are characterized by an indexof the order of five or six. The smoke therefrom is hardly visible.While this is satisfactory to the eye, the result is neverthelesssubstantial air pollution in urban areas.

The fact that the smoke from boilers possesses a Bacharach index of atleast five, even when operating properly, is due to the fact that theheat exchange between the gases of combustion and the circulating wateroccurs across metallic surfaces whose temperature is close to that ofthe water, and therefore much lower than that of the combustion gases.In order to obtain satisfactory efficiency, the fuel burners areadjusted to provide a long flame. Consequently combustion is notcompleted close to the burner proper but extends over a substantial pathlength toward the exhaust stack. At points of greater and greaterdistance from the burner, the influence of the cold metallic heatexchange surfaces becomes greater and greater, with the combustiondeteriorating in consequence so that unburned particles remain in thegases exhausted to the stack. Moreover this tendency worsens with time,so that the Bacharach index, about five for a new boiler, increases withage due to the deposit of soot on the heat exchange surfaces.

A boiler according to the invention includes a combustion chamberoperating at high temperature, the relatively cold metallic water jacketor water tube surfaces of the boiler being insulated within thecombustion chamber from the hot gases of combustion by a layer ofrefractory insulating material having hot spots thereon. It alsocomprises, between the combustion chamber and the stack, in the sense ofcombustion gas flow, a chamber for heat exchange between the gases andthe water jackets or water tubes. The passage of the combustion gasesfrom the first chamber to the second occurs at least in part through afiltering partition made of refractory insulating material.

The preferred insulating material is made of mineral and/or ceramicfibers made up into felts or pads. The hot spots are preferably producedby a grill or grid of refractory metal disposed on the face of the padswhich is exposed to the flames. It is desirable to provide such a gridon both sides of the pads in order to improve their mechanical stabilityand to make it possible to reverse the pads when the grids initiallyexposed to the flames have been consumed.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be furtherdescribed in terms of an exemplary embodiment and by reference to theaccompanying drawings in which the single figure of drawing is aschematic vertical sectional view through a boiler in accordance withthe invention.

DESCRIPTION OF PREFERRED EMBODIMENT The boiler shown in the drawingcomprises an enclosure of parallelepiped shape. This is shown in thedrawing as including vertical front and back walls 2 and 2' and a roof2", which may be made of brickwork for example, or of asbestos coatedonto the iron castings making up the water jacket in a boiler fordomestic heating, to take another example. The enclosure also includesvertical sidewalls, parallel to the plane of the figure and not showntherein, but of the same construction as the front and back walls 2 and2'. It also includes a base plate 3, which may be of iron. A burner isattached to the front wall of the boiler as indicated at l in thefigure. The vertical walls are lined with water jackets as indicated at11, or alternatively with water tubes. The base plate and the verticalwalls are moreover lined, inside the water jackets or water tubes andpart way up their height, with refractory insulating pads as indicatedat 4 made of mineral fiber, the pads being disposed between metallicgrids S of stainless refractory steel. The pads may be made for exampleof kaolin fibers. The insulated combustion chamber 8 thus defined bythese pads is closed at the top by means of a horizontal filteringpartition generally indicated at 6, made of heat insulating materialsuch as ceramic fiber cloth l2 reinforced with one or more metallicgratings 13. An opening 7 is preferably left at one end of thepartition, adjacent one of the vertical walls, to permit escape of theproducts of combustion if the filtering partition should becomeobstructed. The joints between the filtering partition 6 and the pads 4with their grids 5 are carefully sealed with ceramic fiber cement. Theupper portion 9 of the boiler, above the partition 6, thus constitutes aheat exchange chamber in the usual way, bounded in part by the waterjackets or water tubes of the boiler and traversed by the hot gasesbefore they escape through the stack 10 where the Bacharach index may bemeasured.

When flames are established in the combustion chamber 8, the heatinsulating pads 4 which line it retard the transmission of heat to themetallic surfaces of the boiler (i.e., to the metallic surfaces of thewater jackets 11 or of the water tubes) so that the temperature in thischamber and on the walls 4 thereof is much higher than in boilers ofnormal construction. Combustion is accordingly improved. That is, theinternal surfaces of the pads 4 are raised to high temperatures and themetallic grids or gratings 5 on the inner surfaces of these pads, beingof small heat capacity, are raised to red heat promptly upon ignition.The grids 5 thus function as means to ignite the unburned solidparticles which strike against the pads. Under these conditions suchparticles are to a large extent burned, raising the temperature of thewalls of the combustion chamber 8 and further improving combustionthroughout it. Any unburned solids in the gases aspirated out of thecombustion chamber by the draft provided by the chimney are arrested bythe filtering partition 6, which may optionally have imparted thereto acatalytic action to promote burning of such particulate residues.

This cleaning of the smoke is not the only advantage of the invention.The invention encloses the flames and protects the water-gas heatexchange surfaces in the combustion chamber, while raising thetemperature at points more remote from the flame, thus transposingdownstream in the path of the combustion gases a part of the process ofheat exchange with the water. It has however been additionally observedthat the temperature of the exhaust gases in the stack is reduced, whichrepresents, other things being equal, an economy of fuel.

The invention can moreover readily be incorporated into an existingboiler.

By way of example the invention has been applied to two oil-firedboilers of the following characteristics:

Each of these boilers I and II was provided with a combustion chamber inaccordance with the invention by applying to the walls of the fireboxand to the baseplate thereof pads of kaolin wool fiber. These pads were12 to 13 mm. thick and had an apparent density of 0.1 grams per cubiccm. The pads were enclosed between refractory stainless steel grids madeof 0.3 mm. diameter wire with 2.5 mm. width mesh. The combustionchambers of the boilers l and Il so lined were provided, at 30 and 80cm. respectively above their baseplates, with filtering partitions madeof refractory cloth 2.5 mm. in thickness and weighing approximately 1kilogram per square meter. This cloth was woven of threads made up oftwo twisted filaments, each having a metallic core and a coating ofkaolin wool fibers. The cloth was enclosed between refractory metallicgrids similar to those applied to the wall pads. The opening through thepartition had a surface of 560 cm. for the boiler l and of 3.200 cm. forthe boiler ll. Modification of the boilers in accordance with theinvention reduced the Bacharach index from five to zero for the boiler Iand from six to zero for the boiler 11.

The invention thus provides a boiler comprising means defining anenclosure limited at least in part by the walls of a vessel or vessels,such as water tubes or the jackets 11, in the embodiment illustrated,adapted to contain water to be heated. The enclosure may be furtherlimited, as in the embodiment illustrated, by walls 2 and 2' of heatinsulating material outside those vessels, and by a roof 2" and a baseplate 3. The boiler also includes a stack for the exhaust of gases ofcombustion from the enclosure.

A plurality of sheets or pads 4 of refractory heat insulating materialline a part of this enclosure, which part is at least partially closedoff from the remainder of the enclosure by a sheet of refractorymaterial 6, permeable to gases but acting as a filter to arrest unburnedparticles of fuel. The sheets of refractory heat insulating material andthe sheet of gas permeable refractory material may have applied theretoand may be reinforced by grids or gratings of refractory metal.

The gas permeable filter sheet thus divides the enclosure into a fireboxproper 8, wherein fuel is burned with the aid of a burner or firingdevice 1, and a heat exchange chamber 9 whose walls are defined at leastin part by the water-containing vessel or vessels 1 l free of heatinsulating lining.

1 claim:

1. A boiler comprising means definingan enclosure limited at least inpart by the walls of a water-containing vessel, means permitting theexhaust of gases of combustion from the enclosure, refractory heatinsulating material in sheet form lining at least a part of theenclosure, a refractory metallic grating on at least a part of the innersurface of said refractory heat insulating material, fuel burning meansin said part of the enclosure, and a sheet of refractory materialpermeable to gases at least partially closing off said part of theenclosure from the remainder thereof.

2. A boiler according to claim 1 further including a refractory metallicgrating supported on at least a part of the inner surface of the sheetsof refractory heat insulating material.

3. A boiler according to claim 1 including a metallic grating on eachside of said refractory heat insulating material.

4. A boiler according to claim 1 wherein said refractory heat insulatingmaterial in sheet form is made of mineral fibers.

5. A boiler according to claim 1 wherein the sheet of refractorymaterial permeable to gases comprises a cloth woven from refractoryfibers.

6. A boiler according to claim 1 including a refractory grating on theside of the sheet of refractory material permeable to gases adjacent tosaid part of the enclosure.

7. A boiler comprising means defining an enclosure limited at least inpart by the walls of a water-containing vessel, means permitting theexhaust of gases of combustion from the enclosure, refractory heatinsulating material in sheet form lining at least a part of theenclosure, a refractory metallic grating on at least a part of the innersurface of said refractory heat insulating material, fuel burning meansin said part of the enclosure,

and a sheet of refractory material permeable to gases at least partiallyclosing off said part 0 the enclosure from the remainder thereof, saidsheet of refractory material comprising a cloth woven from refractoryfibers.

IUILIAA

1. A boiler comprising means defining an enclosure limited at least in part by the walls of a water-containing vessel, means permitting the exhaust of gases of combustion from the enclosure, refractory heat insulating material in sheet form lining At least a part of the enclosure, a refractory metallic grating on at least a part of the inner surface of said refractory heat insulating material, fuel burning means in said part of the enclosure, and a sheet of refractory material permeable to gases at least partially closing off said part of the enclosure from the remainder thereof.
 2. A boiler according to claim 1 further including a refractory metallic grating supported on at least a part of the inner surface of the sheets of refractory heat insulating material.
 3. A boiler according to claim 1 including a metallic grating on each side of said refractory heat insulating material.
 4. A boiler according to claim 1 wherein said refractory heat insulating material in sheet form is made of mineral fibers.
 5. A boiler according to claim 1 wherein the sheet of refractory material permeable to gases comprises a cloth woven from refractory fibers.
 6. A boiler according to claim 1 including a refractory grating on the side of the sheet of refractory material permeable to gases adjacent to said part of the enclosure.
 7. A boiler comprising means defining an enclosure limited at least in part by the walls of a water-containing vessel, means permitting the exhaust of gases of combustion from the enclosure, refractory heat insulating material in sheet form lining at least a part of the enclosure, a refractory metallic grating on at least a part of the inner surface of said refractory heat insulating material, fuel burning means in said part of the enclosure, and a sheet of refractory material permeable to gases at least partially closing off said part of the enclosure from the remainder thereof, said sheet of refractory material comprising a cloth woven from refractory fibers. 